Generally, paint coating systems in use for painting vehicle bodies and the like are largely constituted by a robot device with an articulated arm, and a coater unit mounted on a distal end of the robot arm of the robot device and provided with an atomizing head for spraying atomized paint particles.
Among paint coating systems of this sort, there is a system providing a paint cartridge replenished by a paint which will be supplied to an atomizing head of the coater unit and can be replaceably attached to a common body which is mounted on a distal end of a robot arm of the robot device (see, for example, Patent Literature 1: Japanese Patent Laid-Open No. 2000-176333).
More particularly, the paint coating system described in the above-mentioned Patent Literature 1 employs a cartridge changer providing a plural number of paint cartridges of each different colors on a mount deck. This cartridge changer is largely constituted by a mount deck on which a plural number of paint cartridges are set, a paint replenisher provided on the mount deck and replenishing consumed paint cartridges, and a cartridge transfer mechanism adapted to transfer a gripped paint cartridge in longitudinal and transverse directions of the mount deck in addition to upward and downward directions.
The cartridge transfer mechanism is composed of a first transfer mechanism having a carriage which is movable on and along a pair of rails extending longitudinally of the mount deck, a second transfer mechanism provided on the carriage of the first transfer mechanism having a carriage which is movable on and along a pair of transversely extending rails, and a third transfer mechanism provided on the carriage of the second transfer mechanism to move a cartridge gripper in upward and downward directions.
At the time of replacing a paint cartridge on a common body of a coater unit, the coater unit is placed at a predetermined cartridge changing position by an action of a robot arm of a robot device, and the robot arm is stopped at that position. In this state, a used paint cartridge at the changing position is picked up and moved upward by means of the cartridge transfer mechanism of the cartridge changer, disconnecting and separating the used paint cartridge from the common body. In the next place, while the common body is fixedly retained in the predetermined changing position by the robot device, a replenished paint cartridge full of paint is transferred to the changing position and set on the common body from above by the cartridge transfer mechanism.
On the other hand, there is a paint coating system providing a plural number of atomizing heads to be replaceably and interchangeably mounted on a common body of a coater unit by means of an atomizing head changer (see, for example, Patent Literature 2: Japanese Patent Laid-Open No. 2001-79463).
In the case of the paint coating system described in the above-mentioned Patent Literature 2, when replacing an atomizing head on a common body of a coater unit, a robot arm of the robot device operates to attach an atomizing head which is mounted on the common body to an atomizing head gripper of an atomizing head changing and washing device. In this state, the common body is lifted up by the robot device to detach the used atomizing head from the common body. On the other hand, after detachment of the used atomizing head, the common body is transferred by a robot device to a head changing position for replacement by another atomizing head which is gripped on the atomizing head gripper.
Further, there is another paint coating system which is composed of a robot device for coating, a coater unit which is mounted on a robot arm of the robot device for spraying atomizing paint, a number of paint cartridges filled with paint of different colors to be replaceably and interchangeably mounted on the robot arm of the robot device, and a cartridge changer adapted to mount a paint cartridge of a respective color replaceably on the robot arm of the robot device (see, for example, Patent Literature 3: International Publication WO 97/34707).
The cartridge changer described in above-mentioned Patent Literature 3 is composed of a rotary table on which a plural number of cartridges are placed in an arcuate formation, and a cartridge gripper which loads a cartridge provided on the rotary table into an opening socket of a robot arm of a robot device.
By the way, in the case of Patent Literature 1 mentioned above, the cartridge transfer mechanism is arranged as an XY table to transfer a paint cartridge in the directions of two orthogonal axes by means of the first transfer mechanism extending in the longitudinal direction and the second transfer mechanism extending in the transverse direction of the first transfer mechanism. This XY table is constructed by mounting heavy rails and carriage of the second transfer mechanism on the first transfer mechanism. Due to heavy weight, the two transfer mechanisms are difficult to start and stop a transfer action speedily. That is to say, the cartridge transfer mechanisms of this type are necessarily required to lower the transfer speed in order to transfer a paint cartridge accurately to a specific position, resulting in a longer changing operation time and a considerable degradation in productivity.
On the other hand, in the case of the paint coating system described in Patent Literature 2 mentioned above, an atomizing head is replaced by moving a coater unit in downward and upward directions relative to an atomizing head gripper which is held in a fixed state. On the other hand, in the case of the paint coating system of Patent Literature 2, a robot arm of a robot device is stopped at a predetermined cartridge changing position to locate and set a coater unit in that position while a paint cartridge is replaced by a cartridge changer.
However, in the case of a robot device which is in use for paint coating operations, with regard to the repeated positioning accuracy in motion control such as moving, stopping, posture and the like of a coater unit which is mounted on a distal end of a robot arm, there is inevitably an error of several millimeters. Therefore, even if the coater unit is moved to a predetermined position for changing an atomizing head or a paint cartridge in response to the same control command after finishing a certain coating operation by the robot device, actually it is often the case that the coater unit is located in a position which is somewhat deviated from the predetermined changing position. Therefore, if the changing operation is carried out depending upon the accuracy of motion control on the part of the robot device alone, this deviation from the predetermined changing position may result in exertion of a forcible load between a common body and the atomizing head or the paint cartridge, shortening the service life of the coater unit by repeated abrasive and damaging contact.
Besides, a robot device is required to be operative with an extremely high degree of accuracy in locating a coater unit in a predetermined specific position at the time of changing a paint cartridge, and, in order to meet this requirement, needs to be installed with high dimensional accuracy despite a considerable increase in cost.
Further, in the case of the paint coating system according to Patent Literature 3, a coater unit which is attached on a robot arm is not equipped with a replaceable paint atomizing head. Therefore, in this case, there is a problem of low productivity because it is impossible to carry out a paint washing operation and a coating operation simultaneously.
In addition, washer is not provided for washing a head portion of a coater unit. This means that it is necessary to wash a robot arm and a coater unit every time when replacing a paint cartridge on the robot arm by a cartridge of a different color.
Furthermore, the paint coating system according to Patent Literature 3, a rotary table on which paint cartridges are placed is rotated by a motor while a cartridge gripper is arranged to move linearly, requiring a large space for installation and a mechanism of complicate construction.